Industrial compressors: learn about the main faults

Industrial Compressors are essential assets, responsible for compressing air, gases or other fluids, changing pressure and controlling flow for specific applications. One of the main examples is the supply of compressed air to pneumatic machines. In industry, much of the use involves lubricated rotary screw compressors. But other types such as piston, spiral or centrifugal models, which can operate with or without lubrication, are also present in the industrial yard. They all fall into the category of positive displacement (or volumetric) compressors.

These assets have some basic components such as hoses, air filters, oil filters, etc. Items that need attention and periodic replacement, characterized by preventive maintenance. However, to extend the useful life and availability of compressors, predictive maintenance based on the condition of critical parts such as bearings and gears is essential. Read on to find out more about the types of compressors, the most common faults and how predictive maintenance can help prevent unplanned downtime.

Read on to find out more about the types of compressors, the most common faults and how predictive maintenance can help prevent unplanned downtime.

Main faults in industrial compressors

Compressors can have some very specific failure modes. These are: liquid return, liquid blowby, lubrication problems, system contamination and high discharge temperature. Find out a little more about each one:

Liquid return

This failure mode occurs when the refrigerant fluid mixes with the lubricant, altering the lubrication capacity. This can happen in both air-cooled compressors and those that use refrigerant fluid with cooling.

Liquid return occurs when the compressor’s suction gas overheats below the required temperature. In this case, the refrigerant gas acts as a detergent and removes the lubricating film.

It is characterized by the complete removal of the lubricating film from the moving parts, causing contact between the parts. Friction can cause parts to wear out, temperatures to rise and even unplanned downtime. This problem can be identified by the increase in vibration levels. In addition, when you examine the parts, you will notice that they are completely clean, free of oil and with no signs of carbonization.

Liquid blowby

The problem occurs when the compressor is working with liquids in the compression chamber. In general, it is caused by the return of refrigerant liquid due to valve problems, reduced load, poor air distribution, etc.

Due to the hydrostatic pressure, the liquid blowby damages the suction valves and the valve plate, damage that can extend to the connecting rod and piston assembly. Visually, the damaged parts show radial grooves, possible cracks or fragmentation.

This failure can also be caused by the return of oil, which causes damage similar to that caused by liquids.

Lubrication problems

Lubrication problems are a common concern in motors, covering a range of issues that directly affect the performance and lifespan of the motor. These include oil dilution or loss and reduced viscosity. 

One of the most recurrent problems is oil dilution. This occurs due to the oil’s affinity with the refrigerant, resulting in the loss of its lubricating capacity when in prolonged contact. This phenomenon mainly affects the connecting rod bearings closest to the oil pump and can lead to wear on the cylinder walls, as well as causing the piston to lock or break. Signs of this problem include metal stains, heavy wear and subtle signs of overheating.

Another problem is oil loss, which can cause significant changes in temperature, especially in the crankshaft, evidenced by discoloration from the excessive heat. This problem can arise due to short cycling, when there is a low coolant charge, excessive foaming of the oil caused by an unsuitable type or dilution of the oil, and prolonged operation with minimal load. It is crucial to be aware of these lubrication problems, as they can have serious consequences for the operation and durability of the motor. Proper maintenance, including choosing the right oil and checking levels regularly, is essential to prevent and mitigate such problems.

High discharge temperature

This failure can cause the compressor to overheat. Among the most common causes is a high compression ratio and low refrigerant charge.  These factors result in an insufficient flow of refrigerant, increasing the temperature of the system and, consequently, of the lubricating oil.

When this problem occurs, there is usually excessive piston wear, as well as visual evidence such as carbonization of the valve plate. In extreme situations, carbonized oil can compromise the movement of the vanes, allowing discharge gas to pass back into the suction. It is essential to monitor and correct high discharge temperatures quickly to avoid serious damage to the compressor and ensure its efficient operation.

Contamination of the system

Among the main contaminants are moisture, copper oxide and dirt.  The presence of moisture can occur during installation or due to the use of contaminated or unsuitable lubricating oils, resulting in corrosion, oxidation, decomposition of the coolant and even deterioration of the components.

In the case of contamination by dirt, any inadequacy in the installation or during the oil change can result in chemical imbalances that alter the structure of the oil, forming acids, incrustations or other forms of combination.

Coppering, on the other hand, can lead to jamming and eventual mechanical breakdown, due to the accumulation of copper particles from the piping system in the crankshaft, bearings and connecting rod/piston assembly. This problem is usually caused by the use of unsuitable lubricants or exposure to high temperatures. In addition to these contaminants, there are other faults that are common to various assets, such as electrical problems, wear or looseness in rotating components, unbalance and gear defects.

Compressor monitoring

To avoid unplanned downtime, it is crucial to identify faults in the early stages in compressors. An effective strategy for this is to install sensors on the compressors to monitor their health. Vibration analysis of this equipment provides important indicators of possible failures, using data collected over time.

In addition, monitoring the pressure measurement of compressors makes it possible to guarantee their performance, ensuring that each compressor operates with the exact demand energy, avoiding premature wear of parts and other related assets.

Strategically positioned on the compressor’s input shaft, near the multiplier gear bearing and in regions close to the bearings, the sensors play a crucial role in the early detection of faults and gear defects in rotating machinery. These continuous monitoring practices are essential for ensuring the efficient and reliable operation of compressors, minimizing the risk of unplanned downtime and reducing corrective maintenance costs.

Read more: How to monitor air compressor with wireless sensors

Each compressor has specific characteristics designed to provide the best performance in certain applications. Read on to find out more about the different categories of compressor:

Categories of industrial compressors

Industrial compressors can be divided into two generic categories related to their basic operating principle: positive displacement compression and dynamic compression.

The positive displacement group includes reciprocating compressors (piston), orbital compressors (scroll) and different rotary types (screw, toothed, vane). Despite the variations in constitution, the operating principle is the same: the chamber opens for air intake and closes for compression, resulting in the air being discharged through the outlet system.

Dynamic displacement compressors include axial or radial flow (centrifugal) turbo compressors, designed for large flow volumes. They have blades that move the air towards the compression impeller, which rotates at high speed (impeller), providing kinetic energy that is converted into pressure energy.

Positive displacement compressors (volumetric)

Reciprocating compressor (piston or reciprocating)

Used in industrial refrigeration, chillers and gas transfer units, this equipment has one or more motor-driven pistons. The movement of the piston is responsible for opening the chamber and increasing the pressure inside the cylinder until the discharge valve opens.

Scroll compressor (orbital or spiral)

Used in various sectors, such as food, refrigeration, air conditioning and transportation, these compressors can be lubricated or oil-free.

Composed of two spirals, one fixed and the other mobile and driven by a motor, the scroll compressor performs compression through the interaction of the spirals. This interaction compresses the air and directs it to the center of the assembly, where it is discharged at the outlet.

Rotary compressor

Widely used in refrigeration, this compressor is also used in the automotive and petrochemical industries. Eccentric rotors rotate inside, creating the pressure needed to compress the air. The movement shrinks the space, compressing the air which is directed to the outlet.

The movement of two rotors is what characterizes this type of compressor. The distinction lies in the shape of the rotors, which gives the compressor its name:

• Screw: a male and a female rotor.
• Toothed: with comma-shaped rotors.
• Vane: the rotor has blade-shaped vanes.

Dynamic displacement compressors

Axial and radial turbo compressors

Applied in oil refineries, chemical plants and other sectors, this compressor is suitable for high flow rates and constant flow.

In the axial compressor, the air moves linearly along the shaft, passing through rows of rotating and stationary blades. In a radial compressor, the air flow is sucked into the center of a rotating impeller with radial blades and then pushed out by centrifugal forces.

In both types, compression occurs by converting kinetic velocity into pressure.

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